Process for producing an item of jewellery

ABSTRACT

A process for producing an item of jewellery, in which a set stone ( 1 ) is fitted into a previously produced recess ( 9 ) in a cast metal body ( 5 ), wherein a part of the setting ( 2 ) is deformed and the stress produced by deformation holds the setting ( 2 ) together with the stone ( 1 ) fast; the recess ( 9 ) of the metal body ( 5 ) acquires in the casting operation its shape which causes deformation of the setting ( 2 ).

[0001] The invention relates to a process for producing an item of jewellery, in which a set stone is fitted into a previously produced recess in a cast metal body, wherein a part of the setting is deformed and the stress produced by deformation holds the setting together with the stone fast.

[0002] The aim of that so-called pre-setting process (see EP 0 346 698 B1) is to make the work of the manufacturer of items of jewellery as easy as possible. In actual fact to secure the stone he now only needs to press the set stone into a suitable recess and the item of jewellery is ready.

[0003] In spite of the apparent simplification in the conventional procedure there are complaint situations which can almost without exception be explained on the basis that the bore produced with a conventional boring tool by the jewellery manufacturer after the casting operation is not of the correct depth or the correct diameter.

[0004] Even if the jewellery manufacturer adequately monitors and controls the boring process, the procedure which is usual nowadays nonetheless presupposes that the cast metal body of the item of jewellery is clamped into a CNC-machine and the holes which serve to receive the stones have to be bored precisely at a right angle to the surface. As it is only possible to produce cylindrical recesses by boring, the manufacturer of pre-set stones is prevented from marketing stones with an oval or angular and in particular quadrangular setting.

[0005] As an alternative to the above-described pre-setting process, the wax melting-out process is known, in which the unset stone is fitted into the wax model and, upon casting of the metal body, is joined thereto (casting-in-place). It will be appreciated that it would also be able to fix a set stone in that way in order to avoid the difficulties involved in producing a bore, but that means that the purpose of marketing pre-set stones would be lost if at best the setting were still to enjoy the advantage that the projections thereof are held fast in positively locking relationship after the casting operation. In addition, use of the pre-setting process is not only intended to facilitate insertion of the stones. On the contrary, an essential advantage of the process is that the fact that the stones are subsequently fixed in frictionally locking engagement in the metal body when already cast makes it possible to avoid damage thereto in the casting operation. The high temperatures involved when fusing in gold (temperatures of between 600 and 1000°) result in physical changes such as for example discoloration effects in relation to many artificial stones and also precious stones. In addition high levels of stress occur due to heating and cooling, which causes some stones to fracture.

[0006] In a process of the kind set forth in the opening part of this specification, the invention avoids the specified problems in that the recess in the metal body receives in the casting operation its shape which causes deformation of the setting.

[0007] The known wax melting-out process can be used for producing the metal bodies, in which respect it is desirable that the insert which fills the recess in the metal body casting process is removed after the casting operation by acid treatment.

[0008] Such a process has certainly already been proposed for setting a precious stone (see U.S. Pat. No. 4,793,045 A). That situation however involved adapting the shape of the recess as far as possible to the shape of the inserted stone which is then held fast by flanging over the edge of the cast setting. In the case of the process according to the invention in contrast the shape of the recess in the metal body precisely does not correspond to that of the pre-produced setting as same is in fact to be deformed by the recess. In order to give the process practical significance it is therefore also appropriate if the manufacturer of pre-produced stones also supplies the associated inserts which in the casting procedure produce the recesses in the item of jewellery, in the correct form, in which case he can now also assume responsibility for success with the entire procedure.

[0009] Details of the process are described hereinafter with reference to the drawing in which:

[0010]FIG. 1 is a view in cross-section,

[0011]FIG. 2 is a side view of a pre-set stone,

[0012]FIG. 3 is a perspective view of a so-called wax tree,

[0013]FIG. 4 shows the associated view in cross-section after being fitted into the casting mould,

[0014]FIG. 5 shows a perspective view of the cast metal body with inserted pins,

[0015]FIG. 6 corresponds to FIG. 5 after removal of the pins, and

[0016]FIG. 7 corresponds to FIG. 5 after insertion of set stones.

[0017] In order to make it easier for jewellery manufacturers to process stones 1 (precious stones or imitations), they are frequently already surrounded, by the manufacturer of the stones, with a metal setting 2 which holds the stone 1 fast for example by a flanging 4. When processing the stones it is only necessary to insert the set stone into a recess which compresses the resilient lugs 3 provided on the setting 2 and thus makes it practically impossible for the stone to be removed.

[0018] In order to produce the necessary recesses in the cast metal body which is to form the carrier for the stones, the invention provides that cores 6 are fitted into the wax model 5′ of the metal body.

[0019] When casting in a mould an article with difficult cavities, undercut configurations or internal contours it is known per se to use cores besides the actual mould. In that respect the core is of such dimensions that it describes the shape and dimensions of the later cavities in the casting. The material thereof is to be so selected that on the one hand in the casting operation it withstands the pressures and temperatures obtaining there without an adverse effect in respect of the shape, and is stable in respect of shape, while on the other hand after hardening it can be dissolved out of the casting quickly and without any problem by using liquids such as lyes, acids and salts. Details about the manufacture of cores of that kind are described for example in EP 0 590 186 B1.

[0020] For casting the metal bodies, a plurality of wax moulds 5′ with inserted cores in the form of the wax tree shown in FIG. 3 are used and surrounded in a chill mould 8 (see FIG. 4) with gypsum 7 or another material which after heating of the mould takes up the wax of the model 5′. The metal, in particular a precious metal, forming the carrier of the stones 1, is cast into the resulting cavity.

[0021]FIG. 5 shows the finished metal body 5 with the cores 6 still fitted therein. After removal thereof, as can be seen from FIG. 6, the metal body 5 has precise recesses 9 into which the set stones as shown in FIGS. 1 and 2 can be pressed, thereby affording the situation shown in FIG. 7. 

1. A process for producing an item of jewellery, in which a set stone is fitted into a previously produced recess in a cast metal body, wherein a part of the setting is deformed and the stress produced by deformation holds the setting together with the stone fast, characterised in that the recess (9) of the metal body (5) acquires in the casting operation its shape which causes deformation of the setting (2).
 2. A process according to claim 1 characterised in that the core (6) which fills the recess (9) in the casting operation for the metal body (5) is removed after the casting step by acid treatment.
 3. A mould insert for the mould used for casting the metal body in the process according to claim 1 characterised in that its surface is identical to that of the inserted setting.
 4. A mould insert according to claim 3 characterised by being in the configuration of a core (6) which is usual for the fine casting of carbon steels using the wax melting-out process and which comprises quartz with additions of zirconium and aluminium oxide.
 5. An item of jewellery which is produced using the process according to claim 1 characterised in that the setting (2) of the stone (1) is non-round, in particular quadrangular. 